The present invention is directed to an aqueous emulsion prepared from a solid organic peroxide, an aqueous size containing the emulsion, and sized glass fibers. More particularly, the present invention is directed to an aqueous peroxide emulsion made from a solid organic peroxide, aqueous treating solution containing same, and sized glass fibers prepared for bonding to polymers in the reinforcement of polymeric materials.
Organic peroxides that decompose by initial cleavage of the oxygen-oxygen bond to produce free radicals act as initiators for vinyl monomers and other vinyl containing materials. There are over fifty different organic peroxides classified into nine major types that are used commercially in the polymer and resin industries. The half-life (T.sub.1/2) which is given as a function of temperature can range for the various peroxides from a short half-life at 0.01 hours at elevated temperature to a longer half-life of 1,000 hours at lower temperatures. The half-life is a measure of the thermal stability of organic peroxides by measuring the time for decomposition of 50 percent of the original amount of peroxide which is a half-life for a first-order reaction. These organic peroxides have been used in the polymerization of vinyl monomers to produce bulk polymers, polymer films and other polymer compositions.
Depending on the thermal stability and other physical characteristics of the particular peroxides, various organic peroxides can be used in different forms when acting as an initiator or curing agent for vinyl polymerization. Some of the organic peroxides such as the highly reactive percarbonates are so unstable that they must be shipped as a frozen solid or an undiluted liquid under refrigeration. Some less reactive organic peroxides, such as lauroyl peroxides and dibenzoyl peroxide are more stable at room temperature and can be activated with greater facility and with less stringent precautions. For example, the relatively more stable benzoyl peroxide, which is a solid at room temperature having a melting point of 106.degree. to 107.degree. C. can be used as granules or crystals or in a thick paste compounded with a phlegmatiser such as tricresyl phosphate. Also, benzoyl peroxide can be used in an aqueous solution as is shown in U.S. Pat. No. 2,343,084 (Smith) wherein the small amount of benzoyl peroxide is dissolved in one or more polymerizable conjugated compounds and may also contain a resin in a solution. This solution can be combined with a water solution of a partially saponified polyvinyl acetate. Also, it has been suggested in U.S. Pat. No. 3,795,630 (Jaspers et al.) to have a chemically stable non-separating organic peroxide composition of an organic peroxide which is a solid at room temperature. The composition is obtained by mixing the solid peroxide, like benzoyl peroxide, with a liquid phlegmatiser like phthalate plasticizers, epoxidized soya bean oil and glycols, and a hydrophobic alkyl group containing silica. In addition, it is shown in U.S. Pat. No. 4,039,475 (Jannes) to have a stable, pumpable aqueous suspension of organic peroxides containing one nonionic emulsifier having a maximum HLB value of 12.5 and a second nonionic emulsifier having a minimum HLB value of 12.5 or a second emulsifier that is anionic.
Organic peroxides such as aryl alkyl peroxide like dicumyl peroxide; ester peroxides and aromatic and aliphatic acyl peroxides have been used in compositions for sizing fibrous materials for use in polymer application as shown in U.S. Pat. No. 3,013,915 (Morgan). These peroxides which have low volatilities and low decomposition temperatures, usually below about 180.degree. F. (82.degree. C.), are deposited from an organic solution. In the composition along with the organic peroxide, there is present a suitable coupling agent.
It is also known as is shown in U.S. Pat. No. 3,837,898 (McCombs et al.) to form a polybutadiene emulsion that contains heat activated curing agents to operate as a catalyst in the size coating on the fibers. The curing agents are the well-known free radical catalysts such as organic peroxides, e.g., benzoyl peroxide, lauroyl peroxide, tert-butyldiethyl peracetate, diacetyl peroxide, as well as inorganic peroxides, such as potassium persulfate. The polybutadiene emulsion is prepared by mixing the polybutadiene with an emulsifying agent and with benzoyl peroxide. To this mixture there is added sufficient water to form an emulsion of the liquid polymer in aqueous medium. The emulsion is then mixed with a mixture of water, glass fiber anchoring agents and a gel agent and the resulting composition is homogenized to form a sizing composition having a solids content of about 2.80 and a pH of about 10.0 to 10.5. The emulsifying agents that can be used are any conventional emulsifying agents, but preferably are the nonionic emulsifying agents such as the polyoxyethylene derivatives of fatty acid, partial esters of sorbitol anhydrides, or the polyoxyethylene derivatives of fatty alcohols, or of the alkyl substituted phenols.
It was recently suggested in U.S. Pat. No. 3,849,148 (Temple) to prepare an aqueous size for glass fibers to be used in reinforcing polyolefin materials wherein the size contained a coupling agent, a heat stable organic peroxide, a nonionic surfactant and usually a lubricant or softener, and optionally a film-former. The heat stable organic peroxide includes organic peroxides having peak decomposition temperatures above about 200.degree. F. (93.degree. C.), for example, alpha alpha' bis(t-butyl peroxy)-diisopropyl benzene, tris(t-butyl peroxy)-diisopropyl benzene, 2,5(t-butyl peroxy)hexane, and 2,5(t-butyl peroxy)hexyne. These heat stable peroxides are used in emulsions with nonionic surfactants such as polyethoxy phenols being prepared and dispersed in water containing a coupling agent. Emulsions prepared at temperatures in the range of 120.degree. F. (49.degree. C.) to 210.degree. F. (99.degree. C.) including isooctyl phenyl polyethoxy ethanol are particularly useful. Other useful nonionic surfactants belonging to the class of polyethoxy phenols are nonyl polyethoxy ethanol and alkyl etherpolyethoxyethanol. Other nonionic surfactants which are useful are polyalkylene glycol ethers, alkyl polyether alcohol and alkyl aryl polyether alcohol. The emulsion is prepared by thoroughly mixing the peroxide initiator with the nonionic surfactant maintaining the temperature of the mixture above the melting point of the free radical initiator. Suitable temperature control is possible by immersing the mixing vessel in a bath of boiling water. After thoroughly mixing the free radical peroxide initiator with nonionic surfactant, water is slowly added to the mixture at a temperature above the melting point of the free radical initiator, preferably in th range of about 140.degree. F. (60.degree. C.) to 150.degree. F. (65.degree. C.) until the emulsion inverts. The emulsion is slowly cooled to ambient conditions by continued water addition. This emulsion is then slowly added to the aqueous mixture containing the coupling agent and the remaining water is added to the mixture to form an aqueous sizing composition for treating glass fibers.
In forming an emulsion for use in a sizing composition for glass fibers, it is necessary to obtain an emulsion with a small particle size and that has shear, shelf and process stability. It is necessary to have an emulsion rather than a dispersion because of the particle size limitation. An emulsion is a two-phase system consisting of two incompletely miscible liquids, the one being dispersed as fine droplets in the other, whereas a suspension is a two-phase system where the dispersed phase is a solid. The particle size and particle size distribution of an emulsion are controlled by such factors as the quantity or the efficiency of the emulsifier, the order of mixing and the type of agitation employed. The stability of an emulsion depends upon such factors as (1) particle size, (2) difference between the densities of the material in the internal phase, which is the liquid broken-up into droplets and of the material of the external phase, which is the surrounding water, (3) the viscosity of the emulsion concentrate, (4) the charges on the particles, (5) choice of emulsifier type and amount of emulsifier used, and (6) the conditions of storage and use, including the temperatures of storage and use, agitation, dilution, and evaporation.
The average particle size and particle size distribution of the emulsion are controlled by such factors as the quantity or the efficiency of the emulsifier, the order of mixing and the agitation employed. The average particle size and particle size distribution of the emulsion are important factors, since large liquid particles or droplets in the emulsion or, for that matter, particles of solid material as in a suspension would not provide an adequate uniform coating to the glass fibers. Also solid particles would abraid the glass fibers, and large liquid particles would cover the surface of the glass fiber in a spotty fashion leaving hiatuses in the coating along the fibers that as a result would not adequately contact the matrix resin to be reinforced.
The emulsion in a sizing composition for glass fibers must be diluted to the extent of approaching a water thin liquid in order to facilitate application to the glass fibers during formation of the fibers. Dilution of an emulsion, especially dilution to the extent of a water thin liquid, can lead to an unstable emulsion. Also, the emulsion in a sizing composition must be shear stable to withstand the mixing of the sizing composition before being applied to the glass fibers. In addition, the emulsion must be shelf stable for periods of three days to more than a week so that the material may be stored before application to the glass fibers. Also, the emulsion must be process stable so it can be applied to the glass fibers.
A problem that has recently surfaced with the use of heat stable, solid organic peroxides is that when they are used in an emulsion which is formed at temperatures above the melting point of the peroxide, the resulting emulsion that is used at temperatures below the melting point of the peroxide tends to have particle sedimentation or particle creaming.
An additional problem with the use of solid organic peroxides in aqueous treating solutions in general is the chance of a violent decomposition reaction during the emulsification process. Since the solid peroxides must be heated to be melted, the use of the elevated temperatures would bring the peroxide closer to its decomposition temperature and a possible violent reaction could occur if the decomposition temperature is reached.
It is an object of the present invention to provide a safer method of preparing an emulsion of a solid organic peroxide that has a melting point and decomposition temperature at elevated temperatures.
It is another object of the present invention to provide an emulsion of a solid peroxide that can be diluted to have a viscosity approaching the viscosity of water and that has improved water stability and improved shelf stability, and improved process stability.
It is an additional object of the present invention to provide an emulsion of a heat-stable organic peroxide that can be used in a sizing composition for glass fibers, where the emulsion is shear stable and shelf stable and process stable within the sizing composition.
It is a further additional object of the present invention to provide processes for preparing an emulsion of a heat-stable organic peroxide and a sizing composition containing same where the peroxide emulsion has improved dilutability, shear stability, and shelf stability, and process stability and fine particle size with a minimum particle size distribution.
It is another further object of the present invention to provide sized glass fiber strands having fibers in the strand with a coating of an aqueous sizing composition containing a coupling agent, an emulsion of heat stable organic peroxide that has improved dilutability, improved shear, shelf and process stability, and a minimum particle size distribution and fine average particle size; and usually a lubricant or softener; and optionally, a film-former.
The average particle size and particle size distribution of the emulsion is an important factor, since large liquid particles in the emulsion, or for that matter, particles of solid material as in a suspension would not efficiently coat the surface of the glass fibers and would be prone to separate from the sizing composition. In addition, solid hard particles in the sizing composition could abrade the glass fibers.